JP2001281470A - Ferromagnetic material-containing optical fiber as well as current sensor and magnetic field sensor using the optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber having excellent magneto-optical characteristics and to provide a high-sensitivity current sensor and magnetic sensor using the optical fiber. SOLUTION: The optical fiber 103 is constituted by including the particles of a ferromagnetic material. The current sensor and magnetic sensor are constituted to have a light source 101 for emitting light, a polarizer 102 for polarizing light to linearly polarized light and an analyzer 104, the optical fiber 103 containing the particles of the ferromagnetic material and a photodetector 105 for detecting the light. The detector 105 is arranged with respective parts in such a manner hat the light emitted from the light source 101 is received through the polarizer 102, the optical fiber 103 and the analyzer 104. Such optical fiber 103 includes the particles of the ferromagnetic material and has the excellent magneto-optical characteristics. The current sensor and magnetic sensor use such optical fiber 103 in a detecting section for current and magnetism and is therefore high in sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber having excellent magneto-optical characteristics. Further, the present invention relates to a high-sensitivity current sensor and a magnetic sensor using the optical fiber.

[0002]

2. Description of the Related Art In general, as a magneto-optical effect, the Zeeman effect (electron energy level splitting) occurs.
), The Faraday effect in which the direction of linearly polarized light rotates (Farad effect)
ay effect), the magneto-optical Kerr effect that changes the direction of polarization of reflected light (magnetic Kerr effect), the Voigt effect of magnetic birefringence, and the Cotton-Mouton effect are known. .

Conventionally, optical fibers have been manufactured from paramagnetic materials such as silica glass and plastic. In particular,
A current sensor that measures a current flowing through a conductor using Faraday rotation and a magnetic sensor that measures a magnetic field of an object to be measured also manufacture a detection unit using an optical fiber made of these paramagnetic materials. For example, in Japanese Patent Application Laid-Open No. 08-054420, a detection unit is configured by winding a silica optical fiber in a coil shape.

[0004]

The paramagnetic material has a problem that the magneto-optical effect is small. In particular,
The current sensor and the magnetic sensor have a problem that the length of the optical fiber of the detection unit needs to be increased. This is because the Faraday rotation angle is proportional to the light traveling direction component of the magnetization and the length of the magnetization passing through the magnetic body. Further, when a twist or the like occurs in the optical fiber, the shape of the optical fiber in the three-dimensional space changes, and the polarization plane rotates by an amount obtained by integrating the twist over the optical path length. For this reason, for example, there is a problem that the shape changes due to the vibration applied to the optical fiber, and the output value changes even though the current value of the test current does not change.

On the other hand, since a ferromagnetic material is an opaque and hard substance, it is difficult to disperse it in silica glass or plastic fiber. Therefore, the present invention is to disperse the ferromagnetic fine particles,
An object of the present invention is to provide an optical fiber having excellent magneto-optical characteristics. Further, it is another object of the present invention to provide a current sensor and a magnetic sensor which are small in size and high in sensitivity by using this optical fiber. An object of the present invention is to provide a current sensor and a magnetic sensor that can suppress the influence on the detection value due to the deformation of the three-dimensional shape by shortening the detection unit.

[0006]

As a first means of the present invention, an optical fiber is constituted by containing ferromagnetic particles. As a second means of the present invention, the optical fiber is constituted by covering one end face with a magnetic film containing ferromagnetic particles.

[0007] As a third means of the present invention, the optical fiber is constituted by, in the second means, making a surface of the ferromagnetic film not in contact with the optical fiber a mirror surface.
As a fourth means of the present invention, an optical fiber, in any one of the means in the first means to the third means, is ferromagnetic, the general formula _{Bi x Y 3-x Fe 5} O 12 (0 < x ≦ 2.0)
Is a bismuth-substituted iron garnet.

According to a fifth aspect of the present invention, there is provided an optical fiber according to any one of the first to third aspects, wherein the ferromagnetic material is selected from the group consisting of the general formula R _{3-x B x} Fe _{5-y MyO 12}
(Where R is the element symbol Y, La, Ce, Pr, Nd, P
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m represents at least one rare earth element selected from the group consisting of m, Yb, and Lu; Bi is an element replacing R;
And M is an element symbol of Al, Ga, Cr, M
n, Sc, In, Ru, Rh, Co, Fc (II), C
u, Ni, Zn, Li, Si, Ge, Zr, Ti, H
represents at least one element selected from the group consisting of f, Sn, Pb, Mo, V and Nb, R and Bi occupy c sites in the garnet crystal structure, and Fe and M represent a and / or occupy d sites,
(0.5 ≦ x ≦ 2, y = 0, 0.5, 1, 1.5).

As a sixth means of the present invention, a current sensor comprises a light source for emitting light, a polarizer and an analyzer for converting light into linearly polarized light, an optical fiber of the first means, and a detecting means for detecting light. And a detector, wherein the detector emits light emitted from the light source,
It is configured by receiving light through a polarizer, an optical fiber, and an analyzer. As a seventh means of the present invention, the current sensor includes a light source that emits light, a beam splitter that branches incident light into two directions, and a polarizing plate that converts light into linearly polarized light;
An optical fiber of any one of the first to fifth means and a detector for detecting light are provided, and light emitted from the light source enters the optical fiber via a beam splitter and a polarizing plate. The incident light is reflected at the end opposite to the incident end of the optical fiber and is emitted from the incident end, and the emitted light is made to enter the detector via the polarizing plate and the beam splitter. It is composed.

According to an eighth aspect of the present invention, there is provided a magnetic sensor comprising: a light source for emitting light; a polarizer and an analyzer for linearly polarizing light; an optical fiber of the first means; And a detector, wherein the detector emits light emitted from the light source,
It is configured by receiving light through a polarizer, an optical fiber, and an analyzer. As ninth means of the present invention, the magnetic sensor includes a light source that emits light, a beam splitter that splits incident light in two directions, and a polarizing plate that converts light into linearly polarized light.
An optical fiber of any one of the first to fifth means and a detector for detecting light are provided, and light emitted from the light source enters the optical fiber via a beam splitter and a polarizing plate. The incident light is reflected at the end opposite to the incident end of the optical fiber and is emitted from the incident end, and the emitted light is made to enter the detector via the polarizing plate and the beam splitter. It is composed.

[0011] In such an optical fiber, bismuth-substituted a ferromagnetic iron garnet _{Y 3-x Bi x Fe 5} O 12 ( hereinafter, abbreviated as "Bi-YIG".) Or aluminum-substituted bismuth iron garnet R _{3 -x Bi x Fe 5-y M} y O 12
(Hereinafter, it is abbreviated as “Al-Bi-YIG”.) The resulting optical fiber has excellent magneto-optical characteristics.
Here, Bi-YIG or Al-Bi-YIG can be dispersed in an optical fiber by making them fine particles.

Since the optical fiber having such excellent magneto-optical characteristics, that is, an optical fiber having a large Faraday rotation angle per unit length, is used for the detecting section, the current sensor and the magnetic sensor can be downsized. And high sensitivity. Further, since the Faraday rotation angle per unit length is large, the optical fiber length of the detection unit can be shortened, so that the influence of the deformation of the three-dimensional shape on the detection value can be suppressed.

The current and the magnetism are determined according to the output value of the detection unit. At this time, it is necessary to consider the angle between the analyzer and the polarizer in the polarization direction.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and description thereof will be omitted.

[0015] (First Embodiment) The first embodiment has the general formula _{Bi x Y 3-x Fe 5} O 12 (0 <x ≦ 2.0) a current sensor (magnetic sensor using the fine particle dispersion optical fiber ) Is an embodiment. (Production of Fine Particles) First, the production of Bi-YIG fine particles will be described.

The fine particles can be produced by various methods. In the present embodiment, the Bi-YIG fine particles are produced by a coprecipitation / sintering method. In this production method, a hydroxide containing these metal ions is precipitated from a mixed aqueous solution of iron nitrate, yttrium nitrate, and bismuth nitrate adjusted to various compositions using aqueous ammonia or aqueous sodium hydroxide. Then, this is heated to be thermally decomposed into an oxide, and further to be crystallized to produce Bi-YIG fine particles. In this coprecipitation / calcination method, the characteristics of the Bi-YIG fine particles depend on the process of forming the precipitate and the process of thermal decomposition.

More specifically, in the present embodiment, the target Bi- is prepared by using iron (III) nitrate nonahydrate, yttrium nitrate hexahydrate and bismuth nitrate pentahydrate in this embodiment.
An aqueous nitrate solution is prepared so as to have a composition of YIG fine particles. For complete dissolution, nitric acid is added to bring the pH to, for example, 3. Then, this aqueous solution is brought to room temperature, for example, 2
At 5 ° C., with vigorous stirring with a mixer, ammonia water is added to make the mixture alkaline, and a hydroxide coprecipitate is obtained.
Here, since the precipitation reaction utilizes a change in solubility product due to neutralization, the composition of the precipitate is affected by the pH. Therefore, in order to make the composition of the completely dissolved raw material aqueous solution and the precipitate match, it is necessary to set the pH to be higher than 8.7 and to precipitate.

Further, the suspension of the precipitate is filtered, separated into a brown slurry-like precipitate and a filtrate, and the brown slurry-like precipitate is washed with water. For example, this washing step is performed by adding and mixing 300 ml of water to the brown slurry-like precipitate, followed by filtration, and this washing step is repeated about five times. After drying, dehydration and crystallization were performed at various temperatures to obtain crystalline fine particles. This is because the hydroxide obtained by the precipitation reaction is in an amorphous state, and thus it is necessary to perform a dehydration reaction and a crystallization reaction by heat treatment in order to obtain Bi-YIG fine particles. Although the formation of fine particles depends on the processing temperature and the processing time, when the processing time is 1 hour, magnetic fine particles can be obtained at a processing temperature of 600 ° C. to 700 ° C. In order to more reliably obtain magnetic fine particles, the processing temperature is preferably 650 ° C. to 700 ° C.

An experiment was conducted to confirm the end of crystallization. As a result, it was found that the crystallization was completed at a processing temperature of 650 ° C. If heat treatment is continued after crystallization, fine particles
Sinter and grow grains. Since it is preferable that the fine particles are small in order to be pulverized and dispersed, it is preferable to perform the heat treatment at a temperature as low as 650 ° C. or less. Bi _1.6 Y _1.4 F
For a composition near e ₅ O _12, from the viewpoint of easy pulverization / dispersion, it is preferable that the processing temperature is about 650 ° C. and the processing time is about 4 hours if optimization is further performed.

The above-mentioned various reagents were all obtained from Kanto Chemical Co., Ltd., special grade. In addition, Bi
_In order to obtain _1.6 Y _1.4 Fe ₅ O ₁₂ fine particles, iron nitrate (II
I) What is necessary is just 17.3 g of 9 hydrate, 4.61 g of yttrium nitrate hexahydrate and 6.67 g of bismuth nitrate pentahydrate.

The particle diameter may be dispersed in a plastic optical fiber as it is. However, in order to suppress the light scattering by the Bi-YIG fine particles and to further reduce the particle diameter, a planetary ball mill may be used. I just need. For example,
10 parts by weight of the above-mentioned Bi-YIG fine powder and water 90
Parts by weight and mixed with a planetary ball mill (Frich P-5,
P-7 type). After standing for several hours, it is filtered and air dried.

It has been found that the ratio of the surface of the magnetic fine particles increases as the particle diameter decreases, and the saturation magnetization also decreases as the particle diameter decreases. Furthermore, it was also found that when the particle size was reduced, if the particle size was less than 5 nm, the ferromagnetic material changed to a paramagnetic material. In the present embodiment, the pulverizing process is performed for about 30 hours so that the particle diameter becomes 50 nm.

(Manufacture of Bi-YIG Fine Particle-Dispersed Optical Fiber) As is generally well known, a method of manufacturing a plastic optical fiber includes manufacturing steps of monomer purification, polymerization, spinning, drawing, and cable processing. Is done.

The Bi-YIG fine particle-dispersed optical fiber of the present embodiment is manufactured by using B
It is manufactured by dispersing i-YIG fine particles. Bi-YI
The G fine particles are chemically inert and can be stably present even in a treatment such as a polymerization reaction. As the plastic material, various translucent plastics such as polymethylene methacrylate, polystyrene, and polyethylene terephthalate can be used, and are selected according to a desired refractive index.

The Bi-YIG particles are not limited to being dispersed throughout the plastic optical fiber, but may be dispersed in a certain range of the plastic optical fiber. (Relationship between Bi-YIG Fine Particle Concentration and Particle Size Concentration and Faraday Rotation Angle) A description will be given of a basic experiment result for designing a plastic optical fiber containing Bi-YIG fine particles.

In the basic experiment, a sheet and a rod containing Bi-YIG fine particles were manufactured. Bi of various Bi concentrations
In the pulverization process, the sheet containing -YIG fine particles was 1 g of Bi-YIG fine particles of various compositions, 0.33 g of an epoxy binder (epo-tek 396, EpoxyTechnology Co.),
Cyclohexanone, 20g, Hyperma MT-1 as dispersant
(ICI Japan) 0.05g was used and the stage was rotated at 360 rpm for 30 hours. Then, the pulverized solution was spread on a polyethylene terephthalate film with a bar coater and dried at 70 ° C. for 4 hours to prepare a film.

FIG. 1 is a diagram showing the relationship between the Faraday rotation angle, the light absorption coefficient and the Bi concentration in the Bi-YIG particle thin film. FIG. 2 is a diagram showing the relationship between the figure of merit and the Bi concentration in a Bi-YIG particle thin film.

[0028] In FIG. 1, the horizontal _{axis, Bi x Y 3-x Fe} e
The Bi concentration in units of x of 5O ₁₂ is shown, and the left vertical axis indicates d
The Faraday rotation angle θF in units of eg / cm and the right vertical axis is the light absorption coefficient α in units of / cm. In FIG. 2, the horizontal axis similarly shows Bi concentration, and the vertical axis shows
It is a figure of merit F in units of deg. Here, the measurement confirmed that the fine particles of each composition had a garnet structure by X-ray diffraction, and the Faraday rotation angle θF was measured with a magnetic polarimeter (JASCO, MOE-07).
The light absorption coefficient α is an ultraviolet-visible spectrophotometer (manufactured by Hitachi, Ltd.
U3210), respectively, using light having a wavelength of 520 nm. The wavelength of 520 nm is a wavelength that shows the maximum Faraday rotation in iron garnet. The strength of the magnetic field is 3 kOe (Oersted). This magnetic field strength of 3 kOe corresponds to 240 kA / m in the SI unit system.

The figure of merit F is the Faraday rotation angle θ.
It is a value obtained by dividing F by the light absorption coefficient α. Therefore, FIG.
It is the figure produced based on FIG. As shown in FIG. 1, the Faraday rotation angle θF increases with an increase in the Bi concentration x, and at x = 1.8, the maximum value is about 3.5 × 10 ³ deg /.
cm. Referring to the result of X-ray diffraction, x = 1.8
At a higher Bi concentration, a garnet structure disorder was observed, which is considered to have resulted in a decrease in the Faraday rotation angle θF. Even at a Bi concentration x = 2.0, the Faraday rotation angle θF is about 1.3 × 10 ^3, which is about two orders of magnitude larger than that of a paramagnetic material, and is still effective.

The light absorption coefficient α gradually increases with an increase in the Bi concentration x, and rapidly increases when x> 1.8. Therefore, as shown in FIG.
At 1.8, the maximum value is about 1.5. As described above, by substituting Bi (0 <x ≦ 2.0), fine particles having excellent magneto-optical characteristics can be obtained, and the fine particles exhibit the most excellent magneto-optical characteristics at a Bi concentration of x = 1.8. Show.

On the other hand, sheets containing Bi-YIG fine particles having various particle concentrations are subjected to Bi _1.8 Y _1.2 F
e ₅ O ₁₂ fine particles 1g, epoxy binder (epo-tek 39
6, Epoxy Technology Co.) 10 g to 0.1 g, cyclohexanone 10 to 25 g, and Hyperma MT-1 (I
CI Japan) 0.05 g was used. Thus, the ratio between the epoxy binder and the fine particles was changed, and the volume concentration of the fine particles was set to 0.05 ≦ z ≦ 0.70. Then, a pulverization treatment was performed at a stage rotation number of 360 rpm for 30 hours, and the pulverized solution was spread and spread on a glass substrate by a spin coating method, and further dried at 70 ° C. for 4 hours.

FIG. 3 is a diagram showing the relationship between the Faraday rotation angle, the light absorption coefficient and the particle concentration in a Bi-YIG particle thin film. FIG. 4 is a diagram showing the relationship between the figure of merit and the particle concentration in a Bi-YIG particle thin film. In FIG. 3, the horizontal axis indicates the particle concentration, and the left vertical axis indicates deg / cm.
Faraday rotation angle 2θF in units of
is the light absorption coefficient α in units of m. In FIG. 4, the horizontal axis similarly shows the particle concentration, and the vertical axis is the figure of merit F in units of deg.

Since the Faraday effect is a characteristic exhibited by Bi-YIG fine particles, it increases as the particle concentration z increases, as shown in FIG. The light absorption coefficient α is
It increases gradually with an increase in the fine particle concentration x. this is,
It is thought to be due to scattering by Bi-YIG fine particles. For this reason, as shown in FIG. 4, the figure of merit F increased with an increase in the particle concentration z, and exhibited a maximum value of 2.2 at 0.40 ≦ z ≦ 0.53.

From the above, in particular, when the particle / binder ratio is 0.1.
In the range of 40 ≦ z ≦ 0.53, light scattering can be reduced optically and the Faraday rotation angle θF can be increased.

Next, experimental results of the rod will be described. The rod is made of Bi _1.5 Y _1.5 Fe ₅ having an average particle size of 46 nm.
O ₁₂ 1.1 mg, epoxy resin material (Epok812, Oken Shoji Co., Ltd.) 15.034 g, Hyperma M as dispersant
T-1 (ICI Japan) 0.0155 was mixed and pulverized and stirred by a planetary ball mill. Thereafter, 13.429 g of an epoxy resin curing agent MNA (Oken Shoji Co., Ltd.),
Add 0.64 g of DMP-30 (Oken Shoji Co., Ltd.)
Stir for an additional 5 minutes. This was cured in a vacuum at 60 degrees for 24 hours and formed into a rod having a diameter of 10 mm and a length of 10 mm. Further, a similar epoxy resin rod containing no Bi-YIG fine particles was prepared as a reference sample. The epoxy resin is a thermosetting resin that causes a polymerization reaction by adding a crosslinking agent to a thermoplastic epoxy compound as a raw material.

Here, for the rod, a thermosetting resin was used for the sake of measurement. It is generally known that ceramic rods (Bi-YIG particles and Al.Bi-YIG particles) are used.
Ferromagnetic material such as particles) and many thermoplastic resins have good wettability, so that the ferromagnetic particles can also be dispersed in the thermosetting resin. FIG. 5 shows the relationship between the Faraday rotation angle θF and the wavelength in the Bi-YIG particle dispersion rod.

FIG. 6 shows the relationship between the Faraday rotation angle θ F and the magnetic field in the Bi-YIG particle dispersion rod. FIG.
In the graph, the horizontal axis represents the wavelength of light expressed in nm, and the vertical axis represents the Faraday rotation angle θF expressed in deg / cm. In FIG. 6, the horizontal axis is the magnetic field expressed in Oe units, and the vertical axis is the Faraday rotation angle θF. In addition, ▲ indicates the measurement result of the Bi-YIG fine particle dispersed rod, □ indicates the measurement result of the reference sample, and ○ indicates the difference between ▲ and □.

As shown in FIG. 5, the wavelength dependency of the Bi-YIG fine particle dispersion rod matches that of the Bi-YIG fine particle, and dispersing the Bi-YIG fine particles increases the Faraday rotation capability of the plastic. I understand.

Then, as shown in FIG. 6, Bi-YIG
The Faraday rotation angle θF of the fine particle dispersion rod is larger in the low magnetic field than that of the reference sample, and the sensitivity of Faraday rotation in the low magnetic field is increased because the Bi-YIG fine particles, which are ferromagnetic fine particles, are dispersed. I understand. (Configuration of Current Sensor) FIG. 7 is a diagram showing a configuration of a current sensor (magnetic sensor) according to the first embodiment and an example of an optical fiber.

The current sensor shown in FIG. 7A has a magnetic sensor configuration. This is because the current sensor measures the Faraday rotation due to the “magnetic field” generated by the current flowing in the conductive band, and thus the current sensor becomes the magnetic sensor as it is. In FIG. 7A, a current sensor (magnetic sensor) is a laser (hereinafter, abbreviated as “LD”).
101, a polarizer 102, a Bi-YIG fine particle dispersed optical fiber 103, an analyzer 104, and a detector (hereinafter, "De
abbreviated as "t". ) 105.

The LD 101 emits, for example, a laser beam having a wavelength of 520 nm. The emitted laser light is applied to the polarizer 10
2 and becomes linearly polarized light and enters the Bi-YIG fine particle dispersed optical fiber 103. This Bi-YIG
The fine particle-dispersed optical fiber 103 is placed so as to intersect with the conduction band 121 through which the test current flows. And Bi-Y
The linearly polarized laser light propagating in the IG particle dispersed optical fiber 103 has its polarization plane rotated by an angle corresponding to the strength of the magnetic field due to the Faraday effect of the magnetic field generated by the test current. The laser light whose polarization plane has been rotated is emitted from the Bi-YIG fine particle dispersed optical fiber 103 and is incident on the Det 105 via the analyzer 104.

The polarization direction of the analyzer 104 is
Placed to match. Therefore, of the laser beam whose polarization plane is rotated by the angle θF by the analyzer 104, the analyzer 1
Since only the component in the polarization direction of No. 04 is emitted, the analyzer 10
The intensity of the laser beam that has passed through 4 is the Faraday rotation angle θF
Is intensity-modulated according to. The Det 105 includes a light receiving element such as a photodiode, for example, and outputs a signal corresponding to the intensity of the received laser light.

On the other hand, the Bi-YIG fine particle-dispersed optical fiber 103 may be an optical fiber in which Bi-YIG fine particles are dispersed throughout the optical fiber as shown in FIG. As shown in (d), an optical fiber in which Bi-YIG fine particles are dispersed at a predetermined position in the optical fiber may be used. As can be seen from FIG. 3, although depending on the Bi-YIG fine particle concentration, the Faraday rotation angle rotates tens of thousands of degrees per cm at a magnetic field strength of 3 kOe.
The i-YIG fine particle dispersing section 111 can obtain a sufficient Faraday rotation even at several μm to several tens μm.

(Correspondence between the present invention and the first embodiment)
The correspondence between the inventions described in claims 1 to 4 and the first embodiment is that the optical fiber corresponds to the Bi-YIG fine particle dispersed optical fiber 103. The correspondence between the invention described in claim 6 and the first embodiment is that the light source corresponds to the LD 101, the polarizer corresponds to the polarizer 102, and the analyzer is the analyzer 1.
04, the optical fiber corresponds to the Bi-YIG fine particle dispersed optical fiber 103, and the detector corresponds to Det105.

The correspondence between the invention described in claim 8 and the first embodiment is that the light source corresponds to the LD 101, the polarizer corresponds to the polarizer 102, the analyzer corresponds to the analyzer 104,
The optical fiber is a Bi-YIG fine particle dispersed optical fiber 103.
And the detector corresponds to Det105. (Function and Effect of First Embodiment) In general, the Faraday rotation angle θF is equal to the length of the Faraday element arranged in the magnetic field (in this embodiment, the Faraday rotation angle θF is smaller than the conduction band 121 of the Bi-YIG fine particle dispersed optical fiber 103). Crossover length) and the strength of the magnetic field. This proportionality constant is called the Verdet constant. Since the strength of the generated magnetic field is proportional to the strength of the test current, the plane of polarization of the laser light emitted from the Bi-YIG fine particle optical fiber rotates Faraday according to the magnitude of the test current. Will be.

For this reason, Bi-Y through the analyzer 104
By measuring the intensity of the laser beam emitted from the IG fine particle optical fiber 103 with Det 105, the current to be measured (magnetic field to be measured) can be measured. It is known that the Verdet constant of a ferromagnetic material is several orders of magnitude larger than that of a paramagnetic material. Therefore, the ferromagnetic material B
By using the Bi-YIG fine particle optical fiber 103 in which the i-YIG fine particles are dispersed, the sensitivity of the current sensor (magnetic field sensor) can be increased. Further, when the sensitivity is the same, the length of the optical fiber serving as the detection unit can be remarkably reduced to several thousandths as compared with a current sensor using a paramagnetic material.

Therefore, unlike the conventional paramagnetic optical fiber current sensor, it is not necessary to wind the optical fiber around the conductor 121 many times, and the installation space is not required. Next, another embodiment will be described. (Second Embodiment) A second embodiment uses the general formula R3 _-xB
i is an embodiment of the _{x Fe 5-y M y O} 12 current sensor using a fine particle dispersion optical fiber (magnetic sensor).

Here, R is the element symbol Y, La, Ce, P
r, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
at least one rare earth element selected from the group consisting of o, Er, Tm, Yb, and Lu, Bi is an element that replaces R, Fe is an element that replaces M, and M is an element symbol of Al or G
a, Cr, Mn, Sc, In, Ru, Rh, Co, Fc
(II), Cu, Ni, Zn, Li, Si, Ge, Zr,
Represents one or more elements selected from the group consisting of Ti, Hf, Sn, Pb, Mo, V and Nb, R and Bi occupy the c site in the garnet crystal structure, and Fe and M
Occupies the a and / or d sites in the garnet crystal structure, and 0.5 ≦ x ≦ 2.0, y = 0, 0.5, 1, 1..
5

The above _{R 3-x Bi x Fe 5} -y M y O 12 as a representative of the fine particles for Al · Bi-YIG particles is described, but, La, Ce, Pr, Nd , etc. Pm in properties similar to Y Since Ga, Cr, Mn, Sc, In and the like have the same properties as Al, the same applies to other elements. Iron garnet is a ferrimagnetic material, and a (16
The difference between the magnetic moments of the iron ions occupying the a) and d (24d) sites corresponds to the externally observable magnetization.
Since the light absorption of iron garnet is due to the iron ions, the Bi-YIG light absorption coefficient can be reduced by replacing the iron ions with an element having no light absorption in a predetermined wavelength region. For example, Al which is an element having no light absorption in the visible region is replaced.

(Production of Al · Bi-YIG Fine Particles)
-Bi-YIG fine particles can be produced by a coprecipitation / sintering method as in the first embodiment. That is, a hydroxide containing these metal ions is precipitated from a mixed aqueous solution of iron nitrate, yttrium nitrate, bismuth nitrate, and aluminum nitrate adjusted to various compositions using aqueous ammonia or aqueous sodium hydroxide. Then, by heating this, it is thermally decomposed into an oxide and further crystallized to produce Bi-YIG fine particles. For the dehydration and crystallization, heat treatment was performed at 700 ° C. for one hour.

[0051] _{Incidentally, Bi 1 Y 2 Al y Fe} 5-y O 12 (y =
0.5) In order to obtain fine particles, 17.24 g of iron (III) nitrate 9 hydrate and 7.26 of yttrium nitrate hexahydrate were used.
g, bismuth nitrate pentahydrate 4.60 g and aluminum nitrate 9 hydrate 1.78 g. Furthermore, this A
As in the basic experiment in the first embodiment, l-Bi-YIG fine particles were mixed with an epoxy binder, pulverized and dispersed in a planetary ball mill for 30 hours, and then mixed with Al-Bi-YIG.
A solution in which fine particles were dispersed was prepared.

(Production of Al-Bi-YIG Fine Particle Optical Fiber) FIG. 8 is a view showing an example of an optical fiber according to the second embodiment. In FIG. 8A, Al.Bi-YI
The G-particle thin-film optical fiber 109 is formed by applying a solution in which the above Al.Bi-YIG fine particles are dispersed to one end surface of a general plastic optical fiber, for example, an optical fiber made of polymethyl methacrylate. Then, the film is naturally dried at room temperature or the like to form a thin film portion 109-b in which Al.Bi-YIG fine particles are dispersed.

Further, as shown in FIG.
A mirror surface portion 109-c is formed on the surface of the Bi-YIG fine particle thin film portion 109-b that is not in contact with the optical fiber, that is, the surface that is in contact with the outside. This mirror surface portion 109-c is, for example,
Al is formed by a vacuum evaporation method. (Relationship between Bi-YIG Fine Particle Concentration and Particle Size Concentration and Faraday Rotation Angle) Next, the results of a basic experiment for designing a plastic optical fiber coated with an Al.Bi-YIG fine particle thin film will be described.

The basic experiment was performed by manufacturing a sheet containing Al.Bi-YIG fine particles. This sheet is
A solution in which Bi-YIG fine particles were dispersed was applied on a glass substrate by a spin coating method. This coating film has a thickness of about 2.0 μm and a volume concentration of the fine particles of about 40%. FIG. 9 is a diagram showing the relationship between the Faraday rotation angle and the light absorption coefficient and the Al substitution amount in the Al.Bi-YIG particle thin film.

FIG. 10 is a diagram showing the relationship between the figure of merit and the amount of Al substitution in an Al.Bi-YIG particle thin film.
In FIG. 9, the horizontal axis represents _{y of} Bi ₁ Y ₂ Aly Fe _5-y O ₁₂ .
Is the unit of Al substitution, the left vertical axis is the light absorption coefficient α in units of / cm, and the right vertical axis is deg / cm
Is the Faraday rotation angle 2θF in units of. In FIG. 10, the horizontal axis similarly indicates the Al substitution amount y, and the vertical axis is the performance index F in units of deg.

Here, the measurement was carried out under the same conditions and equipment as in the first embodiment after confirming that the fine particles of each composition had a garnet structure by X-ray diffraction. As shown in FIG. 9, both the Faraday rotation angle 2θF and the light absorption coefficient α decrease as the Al substitution amount y increases. This is considered that the number of iron ions was sequentially replaced by Al ions.

Here, since the Faraday rotation angle θF and the reduction rate of the light absorption coefficient α are different, the performance index F becomes a maximum value of about 3.2 at y = 0.5 as shown in FIG. As described above, by substituting Fe for Al (0 <y ≦ 1.
5) By doing so, fine particles having excellent transmission characteristics in the visible region and having a Faraday rotation angle larger than that of the paramagnetic material can be obtained.
Shows the best magneto-optical properties.

(Configuration of Current Sensor) FIG. 11 is a diagram showing the configuration of the current sensor according to the second embodiment. FIG.
The current sensor shown in FIG. 1 is also a configuration of a magnetic sensor. In FIG. 11, a current sensor (magnetic sensor) is an LD10
1. Beam splitter 107, polarizer 102, Al.B
i-YIG fine particle thin film optical fiber 109 and Det10
5 is provided.

The laser light emitted from the LD 101 is incident on the polarizer 102 via the beam splitter 107, becomes linearly polarized light, and is incident on the Al.Bi-YIG fine particle thin film optical fiber 109. This Al-Bi-YI
The Al • Bi-YIG fine particle thin film portion 109-b of the G fine particle thin film optical fiber 109 is connected to the conduction band 121 through which the current to be measured flows.
Placed so as to intersect with.

The linearly polarized laser light propagating through the optical fiber portion 109-a in the Al.Bi-YIG fine particle thin film optical fiber 109 is applied to the Al.Bi-YIG fine particle thin film coating portion 109-b. Due to the Faraday effect of the magnetic field generated by the test current, the polarization plane is rotated by an angle β according to the strength of the magnetic field. The laser light whose polarization plane has been rotated is reflected by the mirror surface portion 109-c, and the laser light is again transmitted to the Al / Bi-YIG fine particle thin film portion 109-b.
Then, the polarization plane is further rotated by an angle β corresponding to the strength of the magnetic field.

Since the Faraday effect is a non-reciprocal effect, the reciprocating motion of the Al.Bi-YIG fine particle thin film portion 109-b makes the rotation angle of the polarization plane integrated to 2β. The laser light rotated by 2β propagates again through the optical fiber portion 109-a and enters the polarizer 102. In the laser light rotated by 2β, only the polarization direction component of the polarizer 102 passes through the polarizer 102, the traveling direction is changed by the beam splitter 107, and the laser beam is incident on the Det 105. Det105
Outputs a signal corresponding to the intensity of the received laser beam.

In the above description, the laser beam is applied to the mirror surface portion 109.
Although the light is reflected at -c, it may be an optical fiber without the mirror surface 109-c shown in FIG. Although the reflection intensity of the laser light is lower than that when the light is reflected by a mirror surface, A
This is because the laser beam can be reflected at the end face of the Al-Bi-YIG fine particle thin film portion 109-b due to the difference in the refractive index between the l-Bi-YIG fine particle thin film portion 109-b and, for example, air.

(Correspondence between the present invention and the second embodiment)
The correspondence between the inventions described in claims 2 to 5 and the second embodiment is that the optical fiber corresponds to the Al.Bi-YIG fine particle thin film optical fiber 109. The correspondence between the invention described in claim 7 and the second embodiment is that the light source is the LD 101
And the beam splitter is a beam splitter 107
, The polarizing plate corresponds to the polarizer 102, the optical fiber corresponds to the Al · Bi-YIG fine particle thin film optical fiber 109, and the detector corresponds to the Det 105.

The correspondence between the invention described in claim 9 and the second embodiment is that the light source corresponds to the LD 101, the beam splitter corresponds to the beam splitter 107, the polarizing plate corresponds to the polarizer 102, Fiber is Al-Bi-YIG
Compatible with the fine particle thin film optical fiber 109, the detector is Det.
105. (Operation and effect of the second embodiment) The linearly polarized laser light emitted from the polarizer 102 reciprocates through the Al-Bi-YIG fine particle thin film portion 109-b, so that the polarization plane becomes 2β.
It rotates and is again incident on the polarizer 102. For this reason,
Since only the polarization direction component of the polarizer 102 of the laser light rotated by 2β is transmitted, the Faraday rotation angle 2
The laser light intensity-modulated according to β is emitted from the polarizer 102.

Therefore, by detecting the intensity modulation by the Det 105, the magnitude of the test current can be detected. The Al-Bi-YIG fine particle thin film optical fiber 109 is made of a ferromagnetic Al-Bi-YI
Since it contains G fine particles, the current sensor (magnetic field sensor) can have high sensitivity.

Further, since the portion containing the Al.Bi-YIG fine particles is unevenly distributed at one end of the optical fiber, only the detecting portion can be formed as a probe. The first
In the second embodiment, the plastic optical fiber is used. However, the present invention can be applied to a glass optical fiber.
In the first embodiment, the LD 101 and the polarizer 102
In the second embodiment, an optical isolator may be inserted between the LD 101 and the beam splitter 107. Such an optical isolator can prevent the reflected light from returning to the LD 101 and stabilize the operation of the LD 101.

Then, from the viewpoint of increasing the light coupling rate, a lens may be inserted between each optical component. Next, another embodiment will be described. (Third Embodiment) A third embodiment is based on the general formula Bi _x Y
_This is an embodiment of a _3-x Fe ₅ O ₁₂ (0 <x ≦ 2.0) fine particle dispersed optical fiber.

FIG. 12 is a diagram showing an optical fiber according to the third embodiment and a method for manufacturing the same. In FIG. 12, first, a plastic cylinder 152 (FIG. 12B) is prepared, and a solution in which Bi-YIG fine particles manufactured in the basic experiment of the first embodiment are dispersed in this cylinder is used by using a syringe or the like. Is injected into a predetermined location (FIG. 12C).

Then, the plastic optical fiber 151-a
Then, the plastic optical fiber 151-b is inserted from both the plastic cylinder 152, and the Bi-YIG fine particle dispersed solution phase is sandwiched (FIG. 12D). Here, the outer diameter of the plastic optical fiber 151 is
2 so that the diameter can be inserted. Thereafter, the plastic cylinder 152 is heated. By this heating, B
The solidification of the i-YIG fine particle dispersion solution causes the plastic optical fiber 151-a and the plastic optical fiber 1
The plastic cylinder 152 is fused with the plastic optical fiber 151-a and the plastic optical fiber 151-b (FIG. 12E).

As described above, the Bi shown in FIG.
-The YIG particle dispersion optical fiber 150 is manufactured. (Correspondence relationship between the present invention and the third embodiment) The correspondence relationship between the invention described in claim 1 and claim 3 and the third embodiment is that the optical fiber is a Bi-YIG fine particle dispersed optical fiber 1.
Corresponding to 50.

(Operation and Effect of Third Embodiment) The Bi-YIG fine particle dispersed optical fiber 150 of the third embodiment is made of a ferromagnetic material as described in the first embodiment based on each experimental result. Since certain Bi-YIG fine particles are dispersed, the magneto-optical characteristics are excellent. Note that this Bi-Y
The IG particle-dispersed optical fiber 150 can be used instead of the Bi-YIG particle-dispersed optical fiber 103 in the current sensor (magnetic sensor) shown in FIG.

In the first and third embodiments, the optical fiber in which the fine particles of the general formula Bi _x Y _3-x Fe ₅ O ₁₂ (0 <x ≦ 2.0) are dispersed has been described. R _3-x
It is also possible to disperse the _{Bi x Fe 5-y M y} O 12 fine particles. In the second embodiment, the general formula R _3-x Bi _x
Has been described Fe _5-y M y O ₁₂ optical fiber in which fine particles are dispersed, the general formula _{Bi x Y 3-x Fe 5} O 12 (0 <x ≦
2.0) It is also possible to disperse fine particles.

[0073]

The optical fiber of the present invention is excellent in magneto-optical characteristics because ferromagnetic fine particles are dispersed. Further, since such an optical fiber is used, the Faraday effect is large, so that the current sensor and the magnetic sensor according to the present invention can reduce the size of the detection unit and have high sensitivity. Furthermore, since the current sensor and the magnetic sensor of the present invention can shorten the detection unit, it is possible to suppress the influence of the deformation of the three-dimensional shape on the detection value.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a Faraday rotation angle and a light absorption coefficient and a Bi concentration in a Bi-YIG particle thin film.

FIG. 2 is a figure of merit and Bi of a Bi-YIG particle thin film.
It is a figure which shows the relationship with density.

FIG. 3 is a diagram showing a relationship between a Faraday rotation angle, a light absorption coefficient, and a particle concentration in a Bi-YIG particle thin film.

FIG. 4 is a diagram showing a relationship between a figure of merit and a particle concentration in a Bi-YIG particle thin film.

FIG. 5 is a graph showing a relationship between a Faraday rotation angle θF and a wavelength in a Bi-YIG particle dispersion rod.

FIG. 6 shows a relationship between a Faraday rotation angle θF and a magnetic field in a Bi-YIG particle dispersion rod.

FIG. 7 is a diagram illustrating a configuration of a current sensor (magnetic sensor) and an example of an optical fiber according to the first embodiment.

FIG. 8 is a diagram illustrating an example of an optical fiber according to a second embodiment.

FIG. 9 is a diagram showing the relationship between the Faraday rotation angle and the light absorption coefficient and the Al substitution amount in an Al.Bi-YIG particle thin film.

FIG. 10 is a diagram showing a relationship between a figure of merit and an Al substitution amount in an Al.Bi-YIG particle thin film.

FIG. 11 is a current sensor (magnetic sensor) according to the second embodiment;
FIG. 3 is a diagram showing the configuration of FIG.

FIG. 12 is an optical fiber according to a third embodiment and its manufacturing method.

[Explanation of symbols]

 Reference Signs List 101 laser 102 polarizer 103 Bi-YIG fine particle dispersed optical fiber 104 analyzer 105 detector 107 beam splitter 109 Al / Bi-YIG fine particle thin film optical fiber 150 plastic optical fiber

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Carlos Seiichi San-Eura Mansion 203 F-term (reference) 2G017 AA02 AD12 AD20 BA14 CB04 CB24 CC01 2G025 AA00 AB10 AB13 AC06 2H050 AB43X AC86 AD06

Claims (9)

[Claims] 1. An optical fiber comprising ferromagnetic particles. 2. An optical fiber, wherein one end surface is covered with a magnetic film containing ferromagnetic particles. 3. The optical fiber according to claim 2, wherein a surface of the ferromagnetic film that is not in contact with the optical fiber is a mirror surface. 4. The ferromagnetic material has a general formula Bi _x Y _3-x Fe
The optical fiber according to claim 1, wherein the optical fiber is bismuth-substituted iron garnet having ₅ O ₁₂ (0 <x ≦ 2.0). 5. 5. The ferromagnetic material has a general formula R _{3-x B x} Fe
_{5-y MyO 12} (where R is the element symbol Y, La, Ce, P
r, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
at least one rare earth element selected from the group consisting of o, Er, Tm, Yb, and Lu; Bi is an element that replaces R; Fe is an element that replaces M;
a, Cr, Mn, Sc, In, Ru, Rh, Co, Fc
(II), Cu, Ni, Zn, Li, Si, Ge, Zr,
Represents one or more elements selected from the group consisting of Ti, Hf, Sn, Pb, Mo, V and Nb, R and Bi occupy the c site in the garnet crystal structure, and Fe and M
Occupies the a and / or d sites in the garnet crystal structure, and 0.5 ≦ x ≦ 2.0, y = 0, 0.5, 1, 1..
The optical fiber according to any one of claims 1 to 3, wherein the optical fiber is an aluminum-substituted bismuth-substituted iron garnet that is (5). 6. A light source for emitting light, a polarizer and an analyzer for converting light into linearly polarized light, the optical fiber according to claim 1, and a detector for detecting light, wherein the detector comprises: A current sensor for receiving light emitted from the light source via the polarizer, the optical fiber, and the analyzer. 7. The light source according to claim 1, wherein: a light source for emitting light; a beam splitter for splitting incident light in two directions; An optical fiber, and a detector for detecting light, light emitted from the light source is incident on the optical fiber via the beam splitter and the polarizing plate, and the incident light is the light The light is reflected at the end opposite to the incident end of the fiber and is emitted from the incident end, and the emitted light is
A current sensor, wherein the light is incident on the detector via the polarizing plate and the beam splitter. 8. A light source for emitting light, a polarizer and an analyzer for converting light into linearly polarized light, the optical fiber according to claim 1, and a detector for detecting light, wherein the detector is A magnetic sensor for receiving light emitted from the light source via the polarizer, the optical fiber, and the analyzer. 9. The light source for emitting light, a beam splitter for splitting incident light in two directions, and a polarizing plate for converting light into linearly polarized light, according to any one of claims 1 to 5, An optical fiber, and a detector for detecting light, light emitted from the light source is incident on the optical fiber via the beam splitter and the polarizing plate, and the incident light is the light The light is reflected at the end opposite to the incident end of the fiber and is emitted from the incident end, and the emitted light is
A magnetic sensor, wherein the light is incident on the detector via the polarizing plate and the beam splitter.